Contemporary vehicles include a number of safety systems. One such system, the Anti-Lock Braking System (ABS), monitors wheel rotation during braking to avoid skidding. In addition, ABS signals may be evaluated by a controller to detect other hazardous situations, arising out of varying road conditions. For example, such signals may allow the controller to detect and thus prevent the vehicle from veering off a designated driving course. Alternatively, the controller may implement selective braking of individual wheels when traction experienced at one wheel differs from the others. As a result, a counteracting yawing torque may stabilize the vehicle, reinstating the driver's control.
Similarly, selective braking systems may address a number of other problems. An array of sensors provides the vehicle controller with real-time information about a number of vehicle states. For example, a steering angle sensor supplies information about the current steering angle. An engine management system, ABS rotational speed sensors, and yaw rate sensors all provide information about vehicle status as changes occur. To aid in stability control, accelerometers may detect rotation about the vehicle's longitudinal axis, thus identifying a rollover risk. The sensors allow the controller to intervene incrementally, before conditions reach an emergency level. Oversteer, for example can be corrected by braking the front wheel on the outside of the curve, and understeer can be similarly corrected by braking the rear wheel on the inside of the curve.
Such processes occur relatively rapidly, as conditions develop, and a safety system much achieve immediate chassis stabilization before the vehicle runs out of control. Chassis stabilization may be combined with automatic braking intervention to form a system referred to as Electronic Stability Control (ESC). When automatic steering intervention is added to ESC, the system is generally referred to as ESC II. Steering intervention allows the vehicle to deal with underlying non-homogenous road conditions, conditions of understeer and oversteer, and similar issues.
A recent improvement in such systems is the employment of chassis actuators. Usually, a combination of a controller and one or more sensors actively control chassis settings. Difficulties arise, however, because sensors may fail during operation. If such a failure goes unnoticed, the vehicle may go out of control. To counter that problem, the industry has deployed fault detection systems designed to detect a faulty sensor and transmit that fact to a corresponding controller for evaluation and an appropriate response. The controller may respond by deactivating automatic stabilization and switching to manual control. In such a case, the fault is detected over a period referred to as the detection time. A relatively high detection time may limit the controller's ability to stabilize the chassis, and therefore, that time must not exceed a long threshold value.
Fault detection reaction times generally range from 250-500 μs. That response suffices for conventional, manual chassis stabilization, but it is too slow for stabilization using chassis actuators. For effective automated control, fault detection reaction time should not exceed 150 μs. That response times is achievable, but it tends to be extremely expensive, given the required circuitry and upgraded equipment requirements for signal evaluation, as well as the further requirement for relatively high quality sensors. In addition, sensors must not only be higher quality than those seen in conventional applications, but they also must be installed in parallel to achieve the required levels of reliability.
Thus, a need remains for rapid fault detection means not only to achieve the performance levels required for automated stabilization, but which can achieve such performance in an efficient manner.